In recent years, a transformer, etc., is often provided with an on-load tap changing device that changes a voltage while applying a load current to the transformer, etc. It is important for the on-load tap changing device to ensure the swiftness of a tap changing operation, and thus large changing torque is obtained from an energy-storing unit. According to an energy-storing unit, stored spring force is released at once to rotate a crank at a fast speed, thereby performing a changing operation of a tap changer coupled with the crank within a short time.
The energy-storing unit is provided with a catch which is engaged with a craw formed on the crank and which holds a rotation thereof. The catch is once disengaged from the craw of the crank when releasing spring force, but after the changing operation of the tap changer completes and the crank rotates by a predetermined amount, the catch is engaged again with the craw of the crank. A position where the catch is engaged with the craw of the crank is referred to as a catch standby position.
Meanwhile, when a disturbance or a defect of the tap changer, etc., occurs, and necessary changing torque for the changing operation of the tap changer increases, there may be a case that the rotation amount of the crank becomes insufficient, and thus the craw of the crank does not reach the position of the catch, i.e., the catch does not return to the standby position in some cases. In this case, the catch is unable to be engaged with the craw, and to hold the rotation of the crank. Accordingly, it becomes difficult for the energy-storing unit to store spring force.
Hence, the energy-storing unit is provided with a forcing mechanism (see, for example, Patent Document 1) as an insurance mechanism when the catch does not move to the standby position. The forcing mechanism is a mechanism that forcibly moves the catch to the standby position after the original operation of the energy-storing unit.
Hereinafter, with reference to the perspective views of FIGS. 8 and 9, a detailed explanation will be given of an example conventional energy-storing unit with a forcing mechanism in an on-load tap changing device. As illustrated in those figures, an energy-storing unit is provided with a drive shaft 10 coupled with an electric actuation mechanism (unillustrated), and an eccentric cam 11 is attached to the drive shaft 10.
As illustrated in FIG. 8, the eccentric cam 11 is engaged with a hoist case 12 which is linked with the drive shaft 10 and the eccentric cam 11 reciprocates linearly in synchronization therewith. When the hoist case 12 moving linearly reaches a predetermined position, the hoist case 12 is set to release the engagement of a catch 15 with the craw of a crank 14 to be discussed later.
FIG. 9 illustrates a condition in which the hoist case 12 illustrated in FIG. 8 is detached. Disposed on the bottom face of the hoist case 12 are a spring (unillustrated) and an energy-storing case 13. The energy-storing case 13 reciprocates linearly together with the hoist case 12 through the spring.
The crank 14 that rotates in synchronization with the energy-storing case 13 is coupled to the bottom face of the energy-storing case 13, and a tap changer (unillustrated) is coupled with the crank 14. Moreover, the catch 15 is disposed near the crank 14. The catch 15 is configured to be engaged with the craw of the crank 14 at the standby position.
According to such an energy-storing unit, when the drive shaft 10 rotates upon reception of drive force from an electric actuator mechanism, the eccentric cam 11 rotates together with the rotation of the drive shaft 10. Hence, the hoist case 12 linked with the eccentric cam 11 linearly moves. The hoist case 12 moving linearly applies force to one end of the spring, while causes the energy-storing case 13 contacting the spring to reciprocate linearly. At this time, since the catch 15 at the standby position holds the rotation of the crank 14, the crank 14 does not rotate even though the energy-storing case 13 moves linearly. Hence, the spring is accumulating spring force along with the linear motion of the hoist case 12.
When the hoist case 12 that moves linearly reaches a predetermined position, the hoist case 12 disengages the craw of the crank 14 from the catch 15, and thus the catch 15 is released. Hence, the spring releases the spring force, and thus the energy-storing case 13 moves linearly at fast speed due to the spring force by the spring, and, the crank 14 in synchronization with the energy-storing casing 13 rotates at fast speed. The crank 14 transmits this rotation force to the tap changer, and the tap changer becomes able to perform a fast-speed tap changing operation.
Next, an explanation will be given of the structure of the forcing mechanism built in the energy-storing unit. The forcing mechanism includes a loading cam 16 in a special shape and formed on the eccentric cam 11, and a bearing 19 attached to the energy-storing case 13 (see FIG. 9). When rotating together with the eccentric cam 11, the loading cam 16 abuts the bearing 19, and pushes the bearing 19 in accordance with the shape of such a cam.
According to such a forcing mechanism, the loading cam 16 pushes the bearing 19 while utilizing the rotation torque of the drive shaft 10, thereby causing the sliding motion of the energy-storing case 13, and thus the crank 14 linked with the energy-storing casing 13 is forced to rotate. Hence, if a disturbance, etc., occurs and necessary changing torque for the changing operation of the tap changer increases, it becomes possible to avoid a case in which the rotation amount of the crank 14 becomes insufficient. Accordingly, the catch 15 can surely move to the standby position where the catch is engaged with the craw of the crank 14. According to the energy-storing unit including the above-explained forcing mechanism, even if a disturbance or a breakdown, etc., occurs, the catch 15 is always engaged with the craw of the crank 14, and thus the energy-storing unit can stably store spring force.